The invention relates to a process and a movable machine adapted to tamp railway tracks. A predetermined parameter value, corresponding to the degree of ballast compactness is used in order to vary the tamping process to obtain the same degree of ballast compactness under all the tamped sleepers.
Numerous proposals have been made in this field. It has been admitted for a long time that railway tracks do not present the same faults of position after maintenance operations comprising levelling and tamping as before these operations, it is desirable to tamp the ballast in a manner that results in the same degree of compactness under all the sleepers.
Thus it was proposed in Austrian Pat. No. 194,886 to vary automatically the pressure of the fluid feeding the hydraulic operating motors of the tamping tools of a tamper in function of the value of the resistance which was felt by the tools in the ballast. It was also proposed, in Swiss Pat. No. 333,108, to vary the frequency of the vibrations of the tools of a tamper in function of the local conditions of resistance of the ballast. In another Austrian Patent, No. 198,294, it was proposed to regulate the power of the motor producing the vibrations of the tamping tools in function of fluid pressure existing in the device controlling the tools, which pressure is proportionate to the ballast resistance. Another process illustrated by Swiss Pat. No. 355,170 stopped the tamping at the end of a working cycle when the track began to lift above the normal level under the effect of the force of the ballast beneath the tamped sleeper.
However, not one of the machines described for effecting these diverse processes has been commercially exploited, since their results were unsatisfactory. This emerged from the fact that the proposed adjustments during progress of tamping were a function of the resistance offered by the ballast to the tamping tools. But the value of this resistance varies not only in function of the degree of compactness of the ballast, but likewise as a function of the characteristics thereof, such as its granulation, its hardness, its degree of humidity and its degree of pollution.
It followed that when the resistance of the ballast attained the chosen value during the progress of tamping, the degree of compactness of the ballast could not always be equal under all the tampered sleepers.
The present invention has for its object the provision of a process and a machine for regulating such tamping which avoids this inconvenience by the use of a regulating value, representative of the degree of compactness of the ballast, which is not influenced by the variations of the characteristics of the ballast and which clearly indicates the approach of the maximal degree of compactness.